Conventional performance evaluation of organic electroluminescence elements (organic EL elements) is performed by actually manufacturing organic EL elements and evaluating the same by evaluation methods using voltage-current properties, voltage-luminance properties, current-luminance properties, and the like.
Patent Literature 1 proposes an organic EL element evaluation method which causes a test organic EL element formed on a substrate to emit light by applying a test voltage to the same; measures voltage when the test organic EL element emits light with a predetermined luminance; and compares the measured voltage with a previously set threshold voltage to determine whether the organic EL element has good luminescence properties.
However, this evaluation method cannot perform strict evaluation of organic EL elements including the durability. Even if the above evaluation method provides the same evaluation results as a normal organic EL element evaluation method, drive durability tests can provide different evaluation results.
Accordingly, there is a need for an organic EL element evaluation method which performs easy non-destructive tests in terms of strict performances of an organic EL element, including the durability, within a short time period and can stably supply a lot of organic EL elements having stable device performances.
One of the evaluation methods satisfying such a need is an organic EL element evaluation method by an impedance spectroscopy (IS) method.
The IS method is a measurement method which applies minute sinusoidal voltage signal to an organic EL element; calculates an impedance from the amplitude and phase of the current response signal thereof; and obtains an impedance spectrum as a function of the frequency of the applied voltage signal.
The obtained impedance (Z) is displayed on a complex plane with the frequency of the applied voltage signal as the parameter, which is called a Cole-Cole plot. From the obtained impedance, the modulus (M), admittance (Y), and dielectric constant (ε) as basic transfer functions can be obtained. For example, the modulus (M) is obtained by the following formula (see Non-patent Literature 1, for example).M=jωZ 
In the equation, j indicates an imaginary unit, and ω indicates 2πf (f: frequency).
The transfer function adequate for the analytical purpose can be properly selected from the above four transfer functions, and organic EL elements are evaluated by often using M plots that the modulus is plotted on a complex plane.
For example, an evaluation method is disclosed, which applies a voltage not more than a light emission start voltage to an organic EL element and determines that the organic EL element as the evaluation object is non-defective when n>m is satisfied where m is the number of semicircles in the M plot measured by the IS method and n is the number of organic layers (see Patent Literature 2).
Moreover, another disclosed evaluation method applies a voltage not more than a light emission start voltage to a referential organic EL element, compares the profile of the M plot measured by the IS method with the profile of the M plot of the organic EL element as the test object, and determines that the organic EL element as the test object is non-defective when the difference therebetween is within +/−5% (see Patent Literature 3).